This invention relates to the field of telephone subscriber loops that provide high speed data service and voice service, and, more particularly, to metallic testing of such loops.
A relatively new technology uses the embedded voice telephone infrastructure to provide high speed data service. This service, generally referred to as xe2x80x9cDigital Subscriber Linexe2x80x9d(DSL) service, is available in many markets. DSL is implemented in several different ways, such as asymmetrical DSL (ADSL where upstream and downstream have different bandwidths), symmetrical DSL (SDSL where upstream and downstream have the same bandwidth) and other varieties of services (herein xe2x80x9cXDSLxe2x80x9d or xe2x80x9cDSLxe2x80x9d). Many XDSL technologies provide high speed data service over the current tip-ring pairs by encoding high speed data signals into frequency ranges well above the frequency range that carries both plain old telephone service (xe2x80x9cPOTSxe2x80x9d) or integrated services digital network (ISDN) service. Thus, one subscriber loop comprising a tip-ring pair can provide both voice service and high speed data service.
One problem facing service providers in this fast growing market is loop maintenance. Specifically, most regulatory bodies require that each subscriber loop is tested for power cross, over-voltage, etc. as is known in the art. However, because incumbent voice service providers may be a different entity from the DSL service provider, testing the loop over the entire frequency spectrum (known in the art as xe2x80x9cD.C. to lightxe2x80x9d) requires new and relatively sophisticated and expensive equipment.
Turning now to FIG. 1, a current metallic test system is illustrated in the context of metallic testing of a subscriber loop 5. Subscriber loop 5 subscribes to both voice and DSL services. In a switching office 10, there is a voice switch 12 and a digital subscriber line access multiplexer (DSLAM) 14, which provide voice and data service for subscriber loop 5, respectively. Voice switch 12 is connected to subscriber loop 5 by line card 16 as is known in the art. Line card 16 includes processing unit 18 which sends and receives analog signals over subscriber loop 5 and processes the signals to/from pulse code modulated (PCM) data, as used in the switching network as is known in the art. DSLAM 14 includes a line card 20 which sends and receives data from loop 5 to and from the data network via transceiver 22.
Voice switch 12 and, more specifically, processing unit 18 supports analog signals in the 0-4 kHz band over subscriber loop 5. Generally, DSLAM 14, and more specifically transceiver 22 on line card 20, supports signals in the 32-1,100 kHz range over subscriber loop 5.
DSL introduces frequency and, more importantly, power characteristics that are incompatible with most current art voice service line cards. Conversely, voice service uses DC power with characteristics that interfere with DSL data. Therefore, a splitter 24 is provided in order to filter unwanted characteristics from the subscriber loop 5 for processing at processor 18 on voice line card 16 and DSL line card 20. To enhance the voice signal, splitter 24 includes low-pass filter 26, which attenuates the high voltage of DSL and generally filters out the high frequency DSL signal. To enhance the DSL signal, the DC component of signals on subscriber loop 5 are filtered by a capacitor 28 on line card 20 and a further capacitor 30 in splitter 24.
It is known in the art that voice switches include a voice switch metallic test unit 32 that tests loop 5 for various faults. Metallic test unit 32 is connected to line card 16 via metallic test bus 34. Metallic test bus 34 is connected through a set of relays 36 comprising a normally closed relay 38 and a normally open relay 40. This set of relays 30 is reversed when voice switch metallic test unit 32 tests loop 5 to protect the circuitry of processing unit 18 on line card 16. Likewise, DSLAM 14 includes DSLAM metallic test unit 42 which is connected to line card 20 via metallic test bus 44 to relays 46 including normally closed relay 48 and normally opened relay 50.
In order to effect a usable path through splitter 24 for either metallic test unit 32 or 42, several additional components must be included in splitter 24. For example, in order to test loop 5 from voice switch metallic unit 32, a signature 52 must be present in order to alert voice switch metallic unit 32 of the voltage loss that will occur because of the presence of splitter 24. If signature 52 were not present, then any estimates of broken cable etc. would be incorrect.
Further, a detector 54 needs to be added to splitter 24 in order to detect whether the voice path is currently in use. An additional detector 56 is needed to detect signals from DSLAM metallic test unit 42 which will inform processor 58 that metallic test unit 42 is going to test loop 5. When this occurs, processor 58 closes normally open relay 60 and opens normally closed relay 62 in order to permit testing from DSLAM metallic test unit 42 without interfering with line card 16 on voice switch 12. All of these additional units not only are costly but also require a power supply 64 in order to operate. All of these units also then need to be diagnosed, fused, maintained, alarmed, etc. as is known in the art.
This problem is solved and a technical advance is achieved in the art by a system and method for metallic testing of a subscriber loop that provides voice and DSL services. Voice services are provided by a voice switch and DSL services are provided by a digital subscriber line access multiplexer (DSLAM); each of which includes a metallic test unit. A voice line card in the voice switch has a connection to a first metallic test bus connected to the voice switch metallic test unit via a first set of relays configured to connect the metallic test bus to the subscriber loop and to disconnect the subscriber loop from voice on the line card when testing is performed. A DSL line in the DSLAM card has a connection to a second metallic test bus, which is connected between the DSLAM metallic test unit and the subscriber loop. A second set of relays control the connection of the metallic test bus to the subscriber loop.
In this environment, the voice switch metallic test system is configured to send signals to control the second set of relays to disconnect the DSL line card and to provide metallic tests over the entire wireline spectrum (DC to light). The DSL metallic test unit connected to the second metallic test bus is configured to send signals to control the first set of relays to disconnect the DSL line card and to provide metallic tests from DC to light. Advantageously, a determination is made whether there is traffic on either the voice line or the DSL line prior to metallic testing. The metallic test may then be run and then, for example, a timer may cause the relays to reset to their original state. Further, a detector on each of the line cards may receive out-of-band signaling from the metallic test units and cause the relays to operate.